The present invention relates to a method and an electrolyzer for the production of magnesium and chlorine from salt melt comprising magnesium chloride using magnesium chloride in a solid state.
Feeding of magnesium chloride in solid state to magnesium electrolysis cells is known from earlier patent literature, e.g. U.S. Pat. Nos. 1,567,318, 1,861,798 and 2,396,171. In all these cases a water containing magnesium chloride is used in different hydrated states of MgCl.sub.2 containing from 2 to 5 molecules of H.sub.2 O. It is known that the water in the electrolysis cells reduces the current and power efficiency. It is further known that these water containing salts, e.g. MgCl.sub.2.6H.sub.2 O during normal dehydration decompose upon formation of MgO, HCl, and H.sub.2 O.MgO as an inert constituent settles to the bottom of the electrolysis compartment where, together with a part of the melt, it forms a sludge which accumulates and interferes with cell operation and accordingly has to be regularly removed. HCl, H.sub.2 O-vapor and air accompanying the MgCl.sub.2 -granules attack the graphite anodes and cause considerable dillution of the chlorine gas.
In order to suppress this decomposition reaction it has been suggested in the above mentioned patents to introduce the MgCl.sub.2 -granules at a point close to the anodes, which means in the atmosphere of concentrated Cl.sub.2 liberated at the anodes. This solution had some positive influence on the cell operation, but did not solve the problem regarding anode wear and dilution of the Cl.sub.2 -gas.
German Pat. No. 1.149.538 describes an electrolysis cell with a preheated feeding chamber where magnesium chloride is melted and treated by a gas which suppresses the hydrolysis prior to the transfer of the melt to the electrolysis compartment. This solution gives a rather complicated cell construction and results in a higher energy consumption because of the preheating of the feeding chamber and additional expenses relating to the treatment gas.